My son has a 2014 kx85 we bought the bike from Garrett marchbanks it has pro circuit cylinder carb and head the bike was set up to run mrx-O2 fuel and we swapped heads to run a cheaper c-12 fuel my son ran the bike roughly 15 hours after purchase and it started missing at higher rpm I cleaned carb,replaced top end,replaced reeds,swapped Cdi,stator,coil and it still had a miss on higher rpm' only thing left was replace the crank and that worked now 15 hours later it's doing it again I called PC today and they said it's because I used a hot rod crank and I need to use oem. I Connor keep putting cranks every 15 hours in this bike unless I get lucky and win the lottery. Any answers would be much appreciated